Articular cartilage covers the ends of all bones that form articulating joints in humans and animals. The articular cartilage acts in the joint as a mechanism for force distribution and as a bearing surface between different bones. Without articular cartilage, stress concentration and friction would occur to the degree that the joint would not move easily. Loss of the articular cartilage usually leads to painful arthritis and decreased joint motion.
Articular cartilage is characterized by a structural organization that includes specialized cells (chondrocytes) embedded in an intercellular material which is rich in proteoglycans, collagen fibrils of predominantly type II, other proteins, and water. Cartilage tissue is neither innervated nor penetrated by the vascular or lymphatic systems. However, in the mature joints of adults, the underlying subchondral bone tissue, which forms a narrow, continuous plate between the bone tissue and the cartilage, is innervated and vascularized. Beneath this bone plate, the bone tissue forms trabeculae, containing the marrow. In immature joints, articular cartilage is underlined by only primary bone trabeculae. A portion of the meniscal tissue in joints also consists of cartilage whose make-up is similar to articular cartilage.
Articular cartilage may be damaged by a traumatic injury or from degenerative conditions such as arthritis or osteoarthritis. The inability of articular cartilage to self-repair is a major problem in treating patients having an articular cartilage defect. Over the years a number of treatments have been developed in attempts to repair and/or regenerate articular cartilage. For example, one type of treatment includes subchondral drilling and abrasion. Unfortunately, treatments of this nature are ineffective in the long term because they do not promote formation of new or replacement cartilage tissue or cartilage-like tissue. Instead, these treatments result in the formation of scar or fibrous tissue, which cannot withstand long term joint loading. Thus, although the condition of patients treated using these technique initially improves, eventually it will deteriorate, possibly leading to osteoarthritis.
Another conventional therapy relied on for treating loss of cartilage is replacement with a prosthetic material, such as silicone for cosmetic repairs, or metal alloys for joint realignment. Placement of prostheses is commonly associated with significant loss of underlying tissue and bone without recovery of the full function allowed by the original cartilage, as well as the irritating presence of a foreign body. Other long term problems associated with a permanent foreign body can include infection, erosion, and instability.
More recently, new approaches to cartilage tissue repair have been proposed. One approach is based on implanting or injecting cells into a defect in a patient's cartilage tissue. The implant may include biocompatible synthetic polymeric support structures seeded with chondrocytes, fibroblasts, or bone-precursor cells. Although these approaches have served to further improve treatment of damaged cartilage, there are still a number of problems associated with them. For example, it is difficult to successfully grow the desired quantity and quality of cells on such support structures. Also, the implants may not have sufficient mechanical properties to withstand the loading and other stresses place thereon in the joint.
Accordingly, it would be desirable to provide an improved scaffold that is biocompatible and better facilitates repair and/or regrowth of articular cartilage.